Re: gEDA-user: Exposed copper -- still need to make a pad?

[Larry Doolittle <ldoolitt@xxxxxxxxxxxxxxx>]

On Thu, Sep 27, 2007 at 05:37:18PM +0100, Peter TB Brett wrote:
> On Thursday 27 September 2007 17:06:49 Randall Nortman wrote:
> > On Thu, Sep 27, 2007 at 09:44:36AM -0600, John Doty wrote:
> > > On Sep 27, 2007, at 9:28 AM, Randall Nortman wrote:
> > > > I need to make an exposed area of copper (no soldermask), to act as a
> > > > heat radiator.
> > >
> > > Why no soldermask? I'll bet its infrared emissivity is better than
> > > copper's, making a better radiator. In space, the radiator tape we
> > > use has a thin layer of teflon over the metal for this reason.
> >
> > As sayeth the datasheet, so do-eth the designer!  In fact, any exposed
> > copper is going to be covered in shiny silver stuff (tin/lead/silver,
> > depending on process) during board fab.
> 
> What, not gold?

Gold has even lower infrared emissivity than silver or copper.

OTOH, your radiator has to get quite hot to carry away much
heat by infrared radiation.  Presumably you have some airflow,
either passive (convection) or active (fan-driven).  Then you
want exposed metal, and its emissivity doesn't matter much.

        - Larry


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